Down hole mud motors are used within the oil industry for earth boring operations. These mud motors rotate eccentrically. The eccentric rotation must be converted into concentric rotation in order for the drill bit to function correctly. The current state of the art generally accomplishes this conversion by providing a drive shaft having some type of universal joint connection that connects the down hole motor to a drive assembly rotating the drill bit.
It is generally believed that the drive shaft universal joint assembly cannot tolerate abrasive drilling fluids, thereby having an unacceptable adverse effect on the operational life of the drive shafts. Attempts have been made to effectively seal the universal joint assemblies so as to prolong their operational life. However, these universal joint assemblies do not readily lend themselves to conventional sealing arrangements. Universal joint wear in this instance is generally associated with pitting of the various ball surfaces that characterize these types of universal joint arrangements resulting from the high abrasiveness of the drilling fluids. Replacement of the joint or its components is a costly operation and thus to be avoided if at all possible.
Since the various sealing means have not been very successful, a new approach is clearly needed that would allow the joint to work in an abrasive environment for a significant time without a seal and then be relatively easy and inexpensive to replace as necessary.